1. Field of the Invention
The present invention relates to a video signal processing circuit of a television camera, a video camera, an electronic still camera, or the like.
2. Related Background Art
FIG. 2 is a block diagram showing a construction of a conventional video signal processing circuit.
In FIG. 2, an image pick-up element 3 for receiving a light beam from an object (not shown) through an optical lens 1 and a diaphragm member 2 is an element for converting the light into an electric signal and comprises a solid state image pick-up element such as CCD (charge coupled device), MOS device, or the like. The image pick-up element 3 operates by various kinds of charge transfer pulses from a driving pulse generator 4. An output terminal of the image pick-up element 3 is connected to a sample hold circuit 5. The driving pulse generator 4 generates a charge transfer pulse for driving to the image pick-up element 3 and a sampling pulse for sampling and holding to the sample hold circuit 5. The sample hold circuit 5 samples and holds an output signal from the image pick-up element 3 at a predetermined timing and outputs an analog video signal to an amplifying circuit 6. Next, the video signal whose level was amplified by the amplifying circuit 6 is input to an outline emphasizing circuit 7. the outline emphasizing circuit 7 emphasizes an outline of a change point of the video signal. An output terminal of the outline emphasizing circuit 7 is connected to a white clip level and set up level regulating circuit 8. An output terminal of the regulating circuit 8 is connected to a recording portion 9. A central processing unit (CPU) 10 which is connected to the recording portion 9 and driving pulse generator 4 controls the operation of the apparatus. The CPU 10 controls the generation of pulses from the driving pulse generator 4 and allows the recording portion 9 to record an output signal from the regulating circuit 8.
In the above construction, when the light beam from the object (not shown) enters the image pick-up element 3 through the optical lens 1 and diaphragm member 2, as mentioned above, the video signal obtained by the image pick-up element 3 and sample hold circuit 5 is input to the amplifying circuit 6. The amplifying circuit 6 electrically amplifies the level of the video signal in accordance with an arbitrary amplification factor. A predetermined outline emphasis is executed by the outline emphasizing circuit 7. Subsequently, the regulating circuit 8 regulates the white clip level and set up level of the video signal from the outline emphasizing circuit 7. Thereafter, the video signal is recorded by the recording portion 9.
As mentioned above, in the conventional video signal processing apparatus, the noise portion in the output signal from the sample hold circuit 5 is also amplified by the amplifying circuit 6 shown in FIG. 2, so that there is a problem in that if a predetermined outline emphasis is applied to the output signal from the amplifying circuit 6 by the outline emphasizing circuit 7, noise is generated conspicuously.